1. Field of the Invention
This invention relates to microstrip transmission lines and microstrip transmission line components operating in the millimeter wave region of the frequency spectrum and more particularly to a compact, latching type of microstrip reciprocal phase shifter for use with such microstrip transmission lines and microstrip components.
2. Description of the Prior Art
Reciprocal phase shifters are devices employed to perform a reciprocal phase shift function in many types of RF circuits. In the millimeter wave region of the frequency spectrum, for example, reciprocal phase shifters are employed with phases antenna arrays for radar and communications applications. Additionally, reciprocal phase shifters are utilized in millimeter wave applications as 4-port switchable circulators, power dividers and switches. Since much of the equipment in this region of the frequency spectrum is being designed with planar circuitry utilizing microstrip transmission lines and components because of the substantial savings in size and weight realized, it is essential that microstrip reciprocal phase shifters are available which are capable of being used with this equipment.
In U.S. patent application Ser. No. 152,206, now U.S. Pat. No. 4,816,787, which was filed Feb. 3, 1988 by Richard A. Stern and Richard W. Babbitt, the same applicants as the applicants of the present application, and which was assigned to the same assignee as the assignee of the present application, a microstrip reciprocal phase shifter is described which is especially suited for use with microstrip transmission lines and microstrip components in the millimeter wave region of the frequency spectrum. The phase shifter disclosed therein utilized a rectangular ferrite rod which was mounted on one surface of a length of microstrip transmission line dielectric substrate having an electrically conductive ground plane on the other surface of the substrate. A pair of ramp-shaped transition members were disposed at the ends of the ferrite rod and a length of microstrip conductor was mounted on the top surfaces of the rod, rampshaped members and the substrate and extended from one end of the substrate to the other. A helical coil which extended along the length of the rod and which encircled the microstrip conductor, the rod and the substrate ground plane was energized with a d.c. voltage to produce a unidirectional magnetic field extending along the longitudinal axis of the rod so that the rod functioned as a Reggia-Spencer type of ferrite phase shifter with respect to RF wave energy traveling down the length of microstrip dielectric substrate and passing through the ferrite rod. However, this phase shifter was a non-latching reciprocal phase shifter which required a continuous holding current to maintain a given phase set. Accordingly, for some applications, it would be desirable to have a latching type of microstrip reciprocal phase shifter which would require only the application of a single current pulse to shift the phase shifter from one insertion phase to another insertion phase to thereby produce the desired phase shift. Additionally, it would be desirable to make the phase shifter even more compact by reducing the overall length of the device because the length of the device becomes important when dealing with the microstrip transmission line mode of wave propagation. Finally, it would be desirable to replace the bulky helical coil with a more compact, faster acting control device.